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AIDING REAL-TIME PROCESSING INTEGRITY IN PORTABLE RADIOS UNDER POWER FAIL CONDITIONS

IP.com Disclosure Number: IPCOM000006674D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-22
Document File: 3 page(s) / 206K

Publishing Venue

Motorola

Related People

Dean Banwart: AUTHOR

Abstract

Modem land mobile radios are often equipped with microprocessors or other complex integrated circuits which require signiticant current in order to properly operate. When the power to these circuits is abruptly removed, any processing in progress is aborted. In the past, special support circuits were built to detect such power-loss conditions and supply the processor with volt- age long enough to ensure an orderly shut-down. These additional circuits were costly and required additional space in the products.

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MOTOROLA INC. Technical Developments Volume 17 December 1992

AIDING REAL-TIME PROCESSING INTEGRITY IN PORTABLE RADIOS UNDER POWER FAIL CONDITIONS

by Dean Banwart

ABSTRACT

  Modem land mobile radios are often equipped with microprocessors or other complex integrated circuits which require signiticant current in order to properly operate. When the power to these circuits is abruptly removed, any processing in progress is aborted. In the past, special support circuits were built to detect such power-loss conditions and supply the processor with volt- age long enough to ensure an orderly shut-down. These additional circuits were costly and required additional space in the products.

  An electro-mechanical switch can be built into the release mechanism which locks a portable radio to its battery, The release is built such that the embedded switch must be positively activated before the battery can be removed from the radio. The activation of the switch alerts the embedded processing circuitry in the radio that the battery is about to be removed. The battery attachment mechanics are configured to ensure that sev- eral hundred milliseconds are likely to transpire before the battery is removed. As a result of obtain& this "head- start" advantage, critical processing operations can be completed before the required operating voltage is lost. Such critical operations include, but are not limited to operations which:
* maintain the crypto-integrity of the product.
* write to EEPROM circuits
* maintain other information which is highly sensitive to the user.

BACKGROUND

  Microprocessors, ASICS, and custom/semi-custom integrated circuits in modem radios are required to carry out many processes including some which could be adversely effected by the abrupt removal of power. Among such processes are:

  * Writing to EEPROM. The processor is often required to update configuration data stored in EEPROM technologies. This information often includes the cur-

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rent state of the radio. Since power can be removed at any time, and since EEPROM technology often demands long periods to write to even a single location, writes to EEPROM may be invalidated by loss of power during a write cycles.

  * Securing encryption key variables. In radios equipped with voice and data encryption, the encryption key variables (ii certain high-secure environments) must be stored in a secure manner when the radio is in an "off' or unpowered state. In radios which employ microprocessors or other integrated circuits to manage, route, or store these variables, the registers or memory locations must be totally cleared of such variables (through alternately zeroed, scrambled or enciphered) before the radio is powered down.

  . Some applications are specifically designed to mon- itor and record events which occur at times of power failure, whether planned or accidental.

  Current products often employ internal batteries or large capacitors which supply the necessary time...